The fluidic muscle concept as in U.S. Pat. No. 2,844,126 to Gaylord (1955) has struggled to gain widespread acceptance as an actuator in industry. At least one embodiment of the fluidic muscle has become commercialized in recent decades by Festo AG & Co. Despite several advantages of these actuators over traditional piston-driven linear pneumatic actuators, they have remained obscure.
This paradox is better understood by attempting to design an industrial mechanical system which uses these muscles to produce a rotation. Until now, the implementation of these muscles into a rotary actuator has required either an extensive design effort involving the design of levers and hinges, or the use of hardware which is not suited to the special requirements which arise from the large tensile forces induced by these muscles. Although the concept of a rotary actuator which is activated by a pair of muscles has been extensively explored as in U.S. Pat. No. 7,837,144 to Kothera et al. (2010), U.S. Pat. No. 4,739,692 to Wassam et al. (1988), U.S. Pat. No. 4,615,260 to Takagi et al. (1986), U.S. Pat. Nos. 4,733,603 and 4,819,547 to Kukolj (1988 and 1989 respectively), U.S. Pat. Nos. 6,067,892 and 6,223,648 to Erickson (2000 and 2001 respectively) and U.S. Pat. No. 8,127,659 to Okazaki (2012), there has not existed an easy-to-implement, prepackaged hinge-actuator solution which enables a muscle actuator pair to be easily implemented into a rotary actuator.
There are several modular systems in wide use within the field of industrial automation. One of the most widely used systems is the t-slotted system which has evolved since U.S. Pat. No. 3,513,606 to V. H. Jones (1968) into a large array of extrusion profiles and accessories produced by a variety of manufacturers such as 8020 ® Inc., Bosh Rexroth, and Tslots™. Components exist within these and other standard toolboxes which can be assembled into a rotary actuator, but the large tensile forces applied by pneumatic muscles preclude using standard components to form a long-lasting, robust joint.
The subject of agonist-antagonist paired, tensile driven rotary actuators has been explored in U.S. Pat. No. 3,267,816 to Graham (1966), U.S. Pat. No. 3,448,626 to Yeatman et al. (1969), U.S. Pat. No. 6,860,189 to Perez (2005), and U.S. Pat. No. 7,191,696 to Morr et al. (2007), however these deal with self-contained units which are not generally suitable to accept the relatively long pneumatic muscles and fail to provide a lightweight, simple connection which stabilizes itself under load.
In the field of prosthetic joint replacement, U.S. Pat. No. 3,837,009 to Walker (1974), U.S. Pat. Nos. 4,081,866 6,485,519 to Upshaw et al. (1978), and to Meyers et al. (2002) illustrate simple, self-stabilizing joints which are designed for use with tensile actuation. The concept has not previously extended to modular industrial systems.